Finding Decimal Place in java

[prmccar]

I am creating a program for my java class and I need to find a way to check a double and see if it has a decimal. Is there any way to do this. Here is the code from the program:
import java.util.Scanner;
import java.text.DecimalFormat;
public class MethodsSurprise {
public static void main(String[] args) {
menu();
}
public static void menu() {
Scanner input = new Scanner(System.in);
int choice;
System.out.println("\t1. run the program.");
System.out.println("\t2. end the program.");
choice = input.nextInt();

switch (choice) {
case 1:
input();
break;
case 2:
System.exit(0);
case 3:
System.out.println("The choices are 1 or 2.");
menu();
break;
}
}
public static double input() {
Scanner input = new Scanner(System.in);
double numberGuess;
System.out.println("Choose a number between 1 and 50.");
numberGuess = input.nextDouble();
randomNumber(numberGuess);
return(0);
}
public static double randomNumber(double numberGuess) {
int rNumber;
rNumber = (int)(Math.random() * 10) + 1;
calculations(numberGuess, rNumber);
return(0);
}
public static double calculations(double numberGuess, int rNumber) {
double answer;
double finalAnswer;
answer = (double) numberGuess / (int) rNumber;
finalAnswer = (double) answer / 2;
output(numberGuess, rNumber, answer, finalAnswer);
return(0);
}
public static double output(double numberGuess, int rNumber, double answer, double finalAnswer) {
System.out.println(numberGuess);
System.out.println(rNumber);
System.out.println(answer);
System.out.println(finalAnswer);
menu();
return(0);
}

}

I need it to find if there is a decimal in the number finalAnswer. Any ideas?

 

[Ken g6]

You mean you need to check whether the double "is" also an int? The outlines of a solution appear several times in your code.

Do they need you to consider 2.999999999 == 3 or not?

 

[Broheim]

I only took a quick peek but why don't you just use modulus to see if there's a remainder?

 

[Ancalagon44]

Cast the double to an int, and subtract the int from the original double. If there is any difference, it had a decimal portion.

I know pixel shaders have built in functions such as fract, which return the fractional portion of a number. I dont know if Java has something similar?

 

[BrightCandle]

The problem is doubles can't represent every number accurately, its in the nature of doubles to make it impossible to tell if they are precisely an integer. I could easily input a double that would pass certain logic for looking like an integer under one implementation and not another. Instead of reading a double from the input you should read an integer, that will solve the problem in your program and not have you worrying about the problems with doubles.

 

[Leros]

Should be simple to do with some bit arithmetic.

http://en.wikipedia.org/wiki/Double-precision_floating-point_format

 

[PhatoseAlpha]

Is there some reason (Double%1==0) wouldn't work?

 

[iCyborg]

I think in numerics it's customary to compare doubles to within some small constant. So instead of "x == y", you use "|x-y| < EPSILON"
Here, I'd just do "abs(d - round(d)) < EPSILON". And use round, not floor or ceil.

 

[veri745]

I am creating a program for my java class and I need to find a way to check a double and see if it has a decimal. Is there any way to do this. Here is the code from the program:

import java.util.Scanner;
import java.text.DecimalFormat;
public class MethodsSurprise {
	public static void main(String[] args) {
		menu();
	}
	public static void menu() {
		Scanner input = new Scanner(System.in);
		int choice;
		System.out.println("\t1. run the program.");
		System.out.println("\t2. end the program.");
		choice = input.nextInt();
		
		switch (choice) {
		case 1:
			input();
			break;
		case 2:
			System.exit(0);
		case 3:
			System.out.println("The choices are 1 or 2.");
			menu();
			break;
		}
	}
	public static double input() {
		Scanner input = new Scanner(System.in);
		double numberGuess;
		System.out.println("Choose a number between 1 and 50.");
		numberGuess = input.nextDouble();
		randomNumber(numberGuess);
		return(0);
	}
	public static double randomNumber(double numberGuess) {
		int rNumber;
		rNumber = (int)(Math.random() * 10) + 1;
		calculations(numberGuess, rNumber);
		return(0);
	}
	public static double calculations(double numberGuess, int rNumber) {
		double answer;
		double finalAnswer;
		answer = (double) numberGuess / (int) rNumber;
		finalAnswer = (double) answer / 2;
		output(numberGuess, rNumber, answer, finalAnswer);
		return(0);
	}
	public static double output(double numberGuess, int rNumber, double answer, double finalAnswer) {
		System.out.println(numberGuess);
		System.out.println(rNumber);
		System.out.println(answer);
		System.out.println(finalAnswer);
		menu();
		return(0);
	}

}

I need it to find if there is a decimal in the number finalAnswer. Any ideas?

Using 'code' tags makes it much more readable.

 

[Leros]

I think in numerics it's customary to compare doubles to within some small constant. So instead of "x == y", you use "|x-y| < EPSILON"
Here, I'd just do "abs(d - round(d)) < EPSILON". And use round, not floor or ceil.

That's true. There is usually is an epsilon. I still like analyzing the bits. You're guaranteed to be right that way.